This invention relates in general to valves for controlling fluid flow in a hydraulic or pneumatic system. More particularly, this invention relates to an improved spool valve assembly.
Valves are widely used for controlling the flow of a fluid from a source of pressurized fluid to a load device or from a load device to a pressure vent. Frequently, a pump, or other device, is provided as the source of pressured fluid. The flow of the fluid is selectively controlled by a valve to control the operation of the load device.
One type of valve is a microvalve. A microvalve system is a MicroElectroMechanical System (MEMS) relating in general to semiconductor electromechanical devices.
MEMS is a class of systems that are physically small, having features with sizes in the micrometer range. A MEMS device is a device that at least in part forms part of such a system. These systems have both electrical and mechanical components. The term “micromachining” is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices.
MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today there are many more micromachining techniques and materials available.
The term “microvalve”, as used in this application, means a valve having features with sizes in the micrometer range, and thus by definition is at least partially formed by micromachining. The term “microvalve device”, as used in this application, means a device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or standard (macro) sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve movably supported by a body and operatively coupled to an actuator for movement between a closed position and a fully open position. When placed in the closed position, the valve blocks or closes a first fluid port that is placed in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
One type of microvalve is the micro spool valve. The micro spool valve typically consists of a main valve body disposed in a chamber formed in an intermediate layer of multilayer valve housing. A variety of ports through the layers of the housing provide fluid communication with the chamber. The main valve body is moveable in the chamber to selectively allow fluid communication though the chamber by blocking particular ports depending on the desired result. In operation, a differential pressure is exerted across the main valve body to move the main valve body into a desired position. Typically, the differential pressure is controlled by a pilot valve.
Another type of microvalve, often used as a pilot valve, consists of a beam resiliently supported by the body at one end. In operation, an actuator forces the beam to bend about the supported end of the beam. In order to bend the beam, the actuator must generate a force sufficient to overcome the spring force associated with the beam. As a general rule, the output force required by the actuator to bend or displace the beam increases as the displacement requirement of the beam increases.
In addition to generating a force sufficient to overcome the spring force associated with the beam, the actuator must generate a force capable of overcoming the fluid flow forces acting on the beam that oppose the intended displacement of the beam. These fluid flow forces generally increase as the flow rate through the fluid ports increases.
As such, the output force requirement of the actuator and in turn the size of the actuator and the power required to drive the actuator generally must increase as the displacement requirement of the beam increases and/or as the flow rate requirement through the fluid ports increases.
One specific type of microvalve system is the pilot operated microvalve. Typically, such a microvalve device includes a micro spool valve that is pilot operated by a microvalve of the type as described above. For Example, U.S. Pat. Nos. 6,494,804, 6,540,203, 6,637,722, 6,694,998, 6,755,761, 6,845,962, and 6,994,115 disclose pilot operated microvalves, the disclosures of which are herein incorporated by reference.